Supercomputers typically include a large number of computer cabinets arranged in banks. The computer cabinets typically hold a large number of computer modules positioned in close proximity to each other for increased efficiency. Each computer module can include a motherboard that carries a plurality of processors, routers, and other electronic devices for data and/or power transmission. These devices can generate considerable heat during operation that can damage the devices and degrade performance if not dissipated quickly. To dissipate the heat and avoid damage, supercomputers typically include both active and passive cooling systems.
FIG. 1 is a partially exploded isometric view of a packaged microelectronic device 120 having a heat sink 110 configured in accordance with the prior art. A socket 122 electrically connects the microelectronic device 120 to electrical traces (not shown) on a motherboard 102. The heat sink 110 is held in contact with the microelectronic device 120 by a plurality of screws 114 which extend longitudinally through corresponding coil springs 112. The screws 114 engage threaded sockets 125 protruding from a backplate 126. Threading the screws 114 into the sockets 125 compresses the coil springs 112 against the heat sink 110 and presses the heat sink 110 against the microelectronic device 120 in a “controlled” manner that is intended to provide good thermal conductivity without damaging the microelectronic device 120.
In the prior art example described above, the microelectronic device 120 can represent any one of a number of different devices, such as fast processors, routers, etc., commonly referred to as “high performance devices.” Such devices typically include a large number of electrical connections in a very small volume to prevent signal delays associated with distance. The microelectronic device 120, for example, includes a very fine pitch ball-grid array (BGA) 121 of very small solder balls electrically coupled to corresponding ball pads on a substrate 123. These electrical connections are delicate and susceptible to breakage or damage from stresses caused by the weight of the microelectronic device 120 and movements during shipping, installation, and use. These connections are also very susceptible to damage as a result of pressure exerted by the heat sink 110. As a result, manufacturers of such devices typically limit the pressure that can be applied to the device and the mass that can be attached to the device. Advanced Micro Devices, Inc., for example, specifies a pressure limit of 15 psi and a specified mass limit of 150 grams for certain processors.
One shortcoming of the spring-loaded mounting arrangement illustrated in FIG. 1 is that it can cause the heat sink 110 to exert a nonuniform pressure against the microelectronic device 120. The nonuniform pressure can result from a number of different factors, including spring adjustment, manufacturing tolerances, installation errors, etc. Nonuniform pressure is undesirable because it can cause one corner of the heat sink 110 to press against the microelectronic device 120 with a significantly greater pressure than the other corners. This pressure imbalance reduces the thermal conductivity in the low pressure corners. In addition, the pressure in the high pressure corner may exceed the limit set by the manufacturer, resulting in damage to the BGA 121 and/or degradation in device performance.
Another shortcoming of the heat sink mounting arrangement illustrated in FIG. 1 is that placement of the screws 114 requires cutting back some of the cooling fins. Further, the screws 114 and the coil springs 112 obstruct the flow of cooling air over and around the adjacent cooling fins. Consequently, the screws 114 and the coil springs 112 reduce the heat transfer capacity of the heat sink 110.